Filter media for use in pool filters

ABSTRACT

A sand filter for use with swimming pools includes a tank that has a hollow interior space and a top diffuser for allowing spent pool water to enter the tank and for distributing the pool water inside the tank. The sand filter also includes filter media formed as a bed of material on a bottom of the tank and also includes laterals that are located under the filter media and allow filtered pool water to exit the tank and flow back to the pool. The filter media includes a bed of sand that is disposed on the bottom of the tank and a layer of perlite material that is disposed on a top surface of the bed of sand. The perlite material is a high flow rate, low density perlite material that only contains a trace amount of floaters.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. patent applicationSer. No. 61/227,616, filed Jul. 22, 2009, which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

The present invention relates to swimming pools, and more particularly,to a filter media for use in a sand type swimming pool filter or thelike for reducing bacteria levels (e.g., cryptosporidium levels) and forpromoting improved water characteristics.

BACKGROUND

In many regions of the country, a high percentage of homes have outdoorswimming pools. Pools must be sanitized to prevent growth and spread ofbacteria, viruses, algae and insect larvae that can cause disease.Swimming pool water must contain low levels of bacteria and viruses toprevent the spread of diseases and pathogens between users. This istypically done by using filters, ensuring that the pools have adequateflow rate and chemical disinfectants, such as chlorine, bromine ormineral sanitizers. Pumps and mechanical filters are often used tofilter pathogens out of the water and chemical disinfectants, such asbromine, are used to make the water inhospitable to pathogens.

There are three main types of swimming pool filters, namely, a DE(Diatomaceous Earth) type filter; and a cartridge type filter and a sandtype filter.

DE filters use diatomaceous earth to filter particles out of the water.The filters are composed of plastic grids inside of a plastic type offabric. DE powder coats the grids and filters out tiny debris. If thepressure rises in the filter, the system automatically backwashes,similar to a sand filter, recharging itself with more DE powder. DEfilters can cause some inefficiency and water flow loss because theytend to run at a higher pressure than cartridge filters.

Cartridge filters are considered to be the most economically low inmaintenance. Water runs through a filter inside this particular system,catching any debris. It is very similar to water filtering systems thatare used in homes. These type of pool filters do not clog up as much asthe other pool filters, and two types of filter elements can be used inthe cartridge filter system. The less expensive elements may be cheaperto replace, but they also need replaced more frequently. The moreexpensive elements tend to last longer. Cartridge filters are created torun on lower pressure. They filter out more particles than sand but notas many as DE filters. These filters can be cleaned once or twice duringthe swimming season by simply hosing them off with water.

The most inexpensive of the three kinds of pool filters are the sandfilters. This type of filter works by filtering water through a bed ofsand. Lateral tubes at the bottom of the sand then separate the cleanwater from the dirty water. Water is pushed through the filter sand, andas the filter separates the water, the dirty water is sent to the topwhile the clean water exits through the bottom. Debris can plug up andblock sand filters which causes the pressure to increase in the filterand a drop in the flow of water. This can be fixed by running the systemin reverse to backwash the filter, leaving it cleaned. The filter isthen placed on its rinse mode where it repacks the sand back into thefilter. Maintenance on a sand filter can be done manually every coupleof weeks to keep the sand filter in proper working order. Sand filtersare inexpensive and easy to replace. The downside to owning a sandfilter is that it does not remove small particles that the DE andcartridge filters are capable of removing.

A conventional sand filter includes a vessel or tank that holds the sandand other internal parts and includes a multi port valve or controlvalve which permits a number of different functions to be selected andperformed. For example, the following functions are commonly found on astandard multi port valve: (1) filter: normal filtering and vacuuming;(2) backwash: for cleaning the filter bed of accumulated debris; (3)rinse: use after completing the backwash cycle to ensure all dirty wateris rinsed from the tank to waste; (4) waste: by-passes the tank fordraining or lowering the pool water level and for vacuuming heavy debrisdirectly to the waste line; (5) recirculate: water is recirculatedthrough the valve by-passing the filter; and (6) closed: shuts off theflow from the pump to the filter. The internal parts of the filterinclude: (1) a top diffuser that allows the pool water to enter the tankand distributes the water inside the tank; (2) media (sand) thatcaptures the dirt and debris from the pool water as it flows through;and (3) laterals that are located under the media and allows the poolwater to exit the tank and flow back to the pool.

Relatively little is known about the capabilities of common swimmingpool filters to remove waterborne pathogens. Recent research has foundthat swimming pool sand filters typically remove approximately 25% ofCryptosporidium oocysts. These levels of removal are inadequate toprevent outbreaks of cryptosporidiosis, which is supported by number ofoutbreaks detected and investigated each year by the Centers for DiseaseControl and Prevention (CDC).

Pool filters tend to be designed for keeping swimming pools lookingclear and beautiful, which is not the same as removing all of thewaterborne pathogens. The swimming pool industry has traditionallyrelied on disinfectants, such as chlorine, to control the spread ofwaterborne diseases. The drinking water industry did largely the samething until chlorine-resistant pathogens forced changes in the 1980's(for Giardia) and the 1990's and beyond (for Cryptosporidium). Thechlorine-resistant pathogens forced the drinking water industry to putconsiderable emphasis on filtration optimization to achieve physicalremoval of these pathogens. US drinking water regulations are continuingto become more and more stringent on pathogen removal in order tosafeguard public health. The swimming pool industry could considertaking the same approach.

What is desired is an improved swimming pool sand filter that offers theease and low cost of a conventional sand filter and further offersimproved removal of pathogens, including Cryptosporidium.

SUMMARY

In one embodiment, a sand filter for use with a swimming pool includes atank that has a hollow interior space and a top diffuser for allowingspent pool water to enter the tank and for distributing the pool waterinside the tank. The sand filter also includes filter media formed as abed of material on a bottom of the tank and also includes laterals thatare located under the filter media and allow filtered pool water to exitthe tank and flow back to the pool. The filter media includes a bed ofsand that is disposed on the bottom of the tank and a layer of perlitematerial that is disposed on a top surface of the bed of sand. Theperlite material is a high flow rate, low density perlite material thatonly contains a trace amount of floaters.

In another embodiment, a method of at least substantially eliminatingCryptosporidium organisms from pool water includes the step of: passingpool water through a sand filter to generate filtered pool water. Thefilter includes a filter media that has a bed of sand that is disposedon a bottom of a tank of the filter and a layer of perlite material thatis disposed on a top surface of the bed of sand. The perlite material isa high flow rate, low density perlite material that only contains atrace amount of floaters. In one embodiment, between about 97% and about99% of the Cryptosporidium organisms are removed from the filtered waterby passing the pool water through the sand filter that utilizes theperlite material.

In yet another embodiment, a method is provided for forming asand/perlite layered filter media in a sand filter that is part of aswimming pool that includes a skimmer. The method includes the steps of:(a) adding sand to the bottom of a tank of the sand filter to form a bedof sand; (b) operating the sand filter so that water passestherethrough; and (c) adding a predetermined amount of perlite materialthrough an inlet of the skimmer that is in communication with poolwater, while the sand filter is operating, resulting in the perlitematerial being added as a layer to a top surface of the bed of sand.

It will also be appreciated that the filter media of the presentinvention also serves to “polish” the water and improve thecharacteristics of the water, such as water clarity, etc.

These and other aspects, features and advantages shall be apparent fromthe accompanying drawings and description of certain embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIG. 1 is a side, partial cross-sectional, view of a pool filter systemaccording to one embodiment of the present invention;

FIG. 2 is bar graph showing percent removals of Cryptosporidium-sizedmicrospheres for individual sand filter experiments (with and withoutthe perlite material of the present invention);

FIG. 3 is a bar graph showing mean percentage removals ofCryptosporidium-sized microspheres for sand filter experiments (with andwithout perlite material of the present invention);

FIG. 4 is a bar graph showing log removals of Cryptosporidium-sizedmicrospheres for individual sand filter experiments (with and withoutperlite material of the present invention); and

FIG. 5 is a bar graph showing mean log removals of Cryptosporidium-sizedmicrospheres for sand filter experiments (with and without perlitematerial of the present invention).

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a conventional swimming pool sand filter 100. Thefilter 100 includes a vessel or tank 110 that typically has a domeconstruction. The tank 110 has a top 112 and an opposite bottom 114 witha removable cover or lid 120 being located at the top 112. The filter100 is operatively and fluidly connected to plumbing, generally shown at200, that both delivers dirty pool water to the tank 110 and alsodelivers the filtered water back to the pool. The plumbing 200 includesa top diffuser 210 which is located spaced from the top 112 of the tank110. The top diffuser 210 allows the pool water to enter the tank 110and distributes the water inside the tank 110. The filter 100 alsoincludes filter media 220 which in the case of a sand filter is sand.The sand 220 is formed as a bed on the bottom 114 of the tank 110. Thesand 220 captures the dirt and debris from the pool water as it flowsthrough the tank 110. The filter 100 also includes laterals 230 that arelocated under the media 220 and allow the pool water to exit the tank110 and flow back to the pool.

In accordance with the present invention, the filter media for use inthe sand filter 100 not only includes the bed of sand 220 but it alsoincludes a layer 300 of specially processed perlite. In particular, theperlite layer 300 is disposed on a top surface of the bed of sand 220.The perlite layer 300 is thus the topmost layer of the filter media.

One source of the perlite layer 300 is commercially available fromIndustrial Insulation Group (IIG) of Brunswick, Ga. under the trade namePool Polish. Pool Polish is a perlite material that has been expandedand milled to have a desired, optimal particle size that is particularlywell suited for use in pool filters as the present applicant has found.The technical data for this material is as follows: (1) color: whitefilteraid powder, codex food grade; (2) NSF approved; (3) brightness:GE, dry, 82-85; (4) specific gravity: 2.3; (5) wet apparent density: 8.5to 9.5 lbs/cubic foot; (6) loose weight density: 5.5 to 6.5 lbs/cubicfoot; (7) pH: 7; (8) ignition loss (1 hr @1200° F.); and (9)permeability of 3.25 Darcy units. In one embodiment, the weight of theperlite material is about 0.25 lbs/ft² (or 25 lbs/100 ft²); however, itwill be appreciated that this is merely an exemplary value and otherweight ranges can equally be used so long as the properties disclosedherein are realized.

The perlite layer 300 (e.g., a layer derived from Pool Polish) hasunique properties that provide superior filtering capabilities,including the elimination of potentially harmful bacteria, and inparticular, the perlite layer 300 is a high flow rate, low densityperlite filter powder that only contains trace amounts of floaters.Other conventional perlite materials do not have a combination of theseadvantageous properties. The perlite layer 300 has to have large enoughparticles to bridge the opening of the intersticies between the sandparticles on the surface on which the perlite layer 300 is formed. Theperlite layer 300 has an optimal particle distribution that results inthe formed layer 300 being in the form of a cake layer that does notpenetrate too far into the sand bed. The density of the perlite layer300 is important because the back wash capability of the sand filter 100is limited by design to sweep away small debris but not be too strong towash the sand out of the filter 100. When the filter 100 is back washed,the filter 100 changes the direction of the pump flow and percolates upthrough the sand, thereby washing it. If the perlite layer 300 is formedof a heavier density perlite material as is commonly available or DE,the material will simply roll around with the sand and not get washedout. It appears that the composition/physical shapes of DE (because itis flux calcined) develops an attraction with the sand and also lodgesitself in the intersticies. As is known in the art, floaters areunbroken perlite balls that float naturally and aggressively to thesurface of any liquid. Since the tank 110 is dome shaped, ordinaryperlite, that typically includes a significant percentage of floaters,will not become part of the filter surface (i.e., the top surface of thesand bed) but instead will float in the water toward and to the surfaceof the water. This floating action by the floaters impedes the flow ofthe water on to the perlite layer 300 which is in cake form. Thepresence of floaters can eventually lead to plugging of the dome and theback wash valve at the top of the tank 110. For this reason, ordinaryperlite filter powder contains floaters at high flow level and thereforeis not particularly suited for forming the perlite layer 300 and clearlywill lead to inferior filter performance when compared to theperlite/sand filter media in accordance with the present invention. Evenconventional perlite filter powder that is available with little or nofloats is not suitable for use in the filter media of the presentinvention since the other properties of the powder are inferior and inparticular, the flow rate is too low and the particles are far too smallto effectively work in the filter media of the filter 100 of the presentinvention. This results in clogging of the filter.

The present applicant has accordingly discovered that the perlitedisclosed herein has properties that provide a syngerstic effect whencombined with pool filter materials and provides unexpected results whenincorporated into a pool filter.

In yet another aspect, a method of forming the layered filter media 220is described in detail below.

A pool skimmer, generally shown at 400 in FIG. 1, is part of the overallpool filter system. The pool skimmer 400 is located in the wall of thepool and is connected to the pool's suction pump that is part of thepool's plumbing. The skimmer 400 thus acts to draw water from the poolvia a rectangular aperture in the wall connected through to a devicefitted into one (or more) wall/s of the pool. The internals of theskimmer 400 are accessed from the pool deck through a circular orrectangle lid, about one foot in diameter. On lifting the lid (if thepool is operational) one will see water being drawn from the pool, overa floating weir (operating from a vertical position to 90 degrees angleaway from the pool, in order to stop leaves and debris beingback-flooded into the pool by wave action), and down into a removable“skimmer basket,” the purpose of which is to entrap leaves and otherfloating debris. The aperture visible from the pool side is typically l′0″ wide by 6″ high, which intersects the water midway though the centerof the aperture. However, other sized skimmers, such as “wide angle”skimmers can be used. The skimmer 400 should have a leaf basket orfilter between it and the pump to avoid blockages in the pipes leadingto the pump and filter 100.

In accordance with the present invention, the perlite material isintroduced into the filter tank 110 in a manner that causes the perlitematerial to form a cake-like structure on the top surface of the sandbed without having to access the interior of the tank 110. Morespecifically, the perlite material is introduced through the skimmer ofthe pool. Since the skimmer mechanism immediately feeds the filter andthe perlite material is of the type that can safely pass through theskimmer, the perlite material is easily and effectively introduceddirectly into the tank 110 and the filtering action therein incombination with the specific properties of the perlite material resultsin the perlite material being deposited onto the top surface of the sandbed to advantageously form the cake-like layer of perlite.

Advantageously, the method does not involve the step of opening thefilter tank 110 to access the filter media since this is a timeconsuming, involved process that requires shutting down the filterequipment, etc.

In yet another aspect of the present invention, the perlite layer 300can be provided to the consumer in prepackaged amounts in sealed plasticbags. The package is designed so that it includes instructions that arebased on labeled square footage of the filter. In other words, theamount of perlite material in the package is correlated to a squarefootage of the filter. The user can then simply determine how many bagsto add. When the perlite material comes in prepackaged amounts (e.g., insealed plastic bags), the user simply opens up the package and dumps theperlite material into the skimmer 400, thereby causing the perlitematerial to be layered on the sand bed as described above.

In one embodiment, the perlite is applied in an amount of ¼ lb per sq.ft. of filter surface area. It will be understood that this ratio ismerely exemplary and that other ratios can be used in the practice ofthe present invention.

The following example illustrates the application of the perlite/sandfilter media according to the present invention in a sand type filter.

Example

A 200 gallon (757 L) spa with a sand filter was used at room temperaturefor this exemplary run. The filter and the pump werecommercially-available products (Pentair Challenger 3 HP pump; PentairTriton TR40 sand filter). Only one type of precoat media was used inthis run (Industrial Insulation Group, LLC, Tech-Flo Perlite Filteraid,permeability 3.25 Darcys). The spa system was pumped water at 38 gpm(144 L/min), and the flow was measured with a digital flow meter(Scienco Products, Model SEM-40 electronic flow meter) and controlledwith a 2-inch (51 mm) diameter PVC ball valve. Inline feed of themicrosphere suspensions was made possible by a digital peristaltic pump(Watson Marlow, Model 505Di) feeding directly into the PVC pipe justupstream of the pump. The microsphere suspensions were prepared in a 1-Lglass Erlenmeyer flask of simulated pool water and stirred continuouslywith a magnetic stirrer (Barnstead/Thermolyne, Cimarec® Digital StirringHot Plate) and Teflon®-coated stir bar prior to and during the runs.

Simulated pool water was created for each experiment from 200 gallons(757 L) of Charlotte, N.C. (US) tap water supplemented with sodiumbicarbonate to an alkalinity of 150 mg/L as CaCO₃, with calcium chlorideto a hardness of 250 mg/L as CaCO₃, with sodium hypochlorite to a freechlorine concentration of 2 mg/L, with hydrochloric acid to a pH of 7.5,and with a mixture of artificial sweat and urine to a final totalorganic carbon concentration of 20 mg/L as C. Runs were performed induplicate, and duplicate samples were collected during each run from thefilter influent and filter effluent pipes. Approximately 2×10⁷ YGfluorescent carboxylate-modified polystyrene microspheres (Polysciences,Inc, Cat. #16592, 4.869 μm, std. dev. 0.246 μm) were used in each run.The 1 L microsphere suspension was fed in at 50 mL/min during theexperiment to achieve a filter influent concentration of approximately6.95 microspheres per mL, of water Influent samples of 50 mL werecollected in sterile 50 mL conical-bottomed plastic centrifuge tubes(Falcon® Blue-Max™ Order #352074), and the volume of the effluentsamples varied from 50 mL to 500 mL with the larger samples collected inWheaton glass media bottles.

Samples were stored at 4° C. after collection and prior to analysis.Sample volumes analyzed were adjusted to obtain between 10 and 150oocysts and/or microspheres per sample. Samples were filtered through3-μm polycarbonate track-etched (PCTE) filters (GE, Order #K30CP02500)in 25-mm glass microanalysis filter funnels (Millipore Model xx10 02500) by a regulated 3-place vacuum manifold. The filters were mounted onglass micro slides (Gold Seal® Order #3058) with one drop of polyvinylalcohol-DABCO solution (Freer, 1984) and a glass cover slip (Corning,25-mm square, No. 1.5) for enumeration under epifluorescent microscope(Zeiss Standard 25 microscope) at 100× total magnification. Thefluorescent filter set had a 450-490-nm excitation wavelength range, a510-nm dichroic filter, and a 520-nm emission filter. The spa system wasthoroughly cleaned between runs with a minimum of three drain-and-fillrinses with recirculation at 60 gpm (227 L/min), and samples werecollected prior to seeding in each run to measure any potentialcarryover between runs. The run schedule was staggered between sand andsand-perlite runs in successive experiments.

Filter removal percentages are shown in FIG. 2 for each experiment inthis study. The results demonstrated that a standard sand filter(without perlite) was not very efficient at removingCryptosporidium-sized particles with removals ranging from 6 to 41% witha mean of only 19% (as shown in FIG. 2). The same sand filter with athin layer of perlite media in accordance with the present invention ontop of the sand bed demonstrated good removal capabilities ofCryptosporidium-sized particles with mean removals ranging from 97 to99% with a mean of 98.4% as shown in FIGS. 2 and 3. The error bars inFIG. 3 represent one standard deviation of the data above and below themean value.

FIGS. 4 and 5 display the same data as FIGS. 2 and 3, but the removalsare calculated and displayed as Log removals instead of percentages. Theresults showed that a standard sand filter (without perlite) was againnot very efficient at removing Cryptosporidium-sized particles withremovals ranging from 0.03 to 0.23 Log with a mean of 0.09 Log. The sandfilter with a thin layer of perlite media on top demonstrated goodremoval capabilities of Cryptosporidium-sized particles with meanremovals ranging from 1.59 to 2.10 Log with a mean of 1.79 Log. Theerror bars represent one (Log transformed) standard deviation of thedata above and below the mean.

The above results indicate that adding the perlite material disclosedherein (in the amount of ¼ lb per sq. ft. of filter surface area) to asand filter significantly improved the removal of Cryptosporidium-sizedparticles. Removals averaged less than 20% through sand filters withoutperlite, but the mean removal increased to greater than 98% when perlitewas added to the filter. The filter loading rates remained constant inthis example at 20 μm/ft².

As used herein, the term “trace amount of floaters” refers to perlitematerials that have less than 1% floaters by volume, preferably lessthan 0.5% floaters and more preferably less than 0.25% floaters.

As used herein, the term “substantially eliminating” refers to anelimination of 97% or greater in the total count of an object/element,such as bacteria.

In yet another aspect of the present invention, a cost savings inelectricity charges is realized since the pool filter 100 does not haveto be run as often and/or can be run for shorter treatment/filteringtimes due to the improved filtering capabilities of the filter of thepresent invention. This is a result of the increased effectiveness ofthe filter 100 in filtering unwanted matter, including theabove-described pathogens. The sand filter of the present invention isalso cleaner and safer than conventional sand filters.

It will also be appreciated that the filter media of the presentinvention also serves to “polish” the water and improve thecharacteristics of the water, such as water clarity, etc. As a result,the filter media has the commercial product name of “Pool Polish.”

While the invention has been described in connection with certainembodiments thereof, the invention is capable of being practiced inother forms and using other materials and structures. Accordingly, theinvention is defined by the recitations in the claims appended heretoand equivalents thereof.

1. A sand filter for use with swimming pools comprising: a tank that hasa hollow interior space; a top diffuser for allowing spent pool water toenter the tank and for distributing the pool water inside the tank;filter media formed as a bed of material on a bottom of the tank; andlaterals that are located under the filter media and allow filtered poolwater to exit the tank and flow back to the pool; wherein the filtermedia includes a bed of sand that is disposed on the bottom of the tankand a layer of perlite material that is disposed on a top surface of thebed of sand, the perlite material being a high flow rate, low densityperlite material that only contains a trace amount of floaters.
 2. Thesand filter of claim 1, wherein the perlite material has a specificgravity of about 2.3; a wet apparent density between about 8.5 to 9.5lbs/cubic foot; a loose weight density between about 5.5 to 6.5lbs/cubic foot; and a Darcy units of about 3.25.
 3. The sand filter ofclaim 1, wherein a weight of the perlite material is about 0.25 lbs/ft².4. The sand filter of claim 1, wherein the layer of perlite materialcomprises a cake structure of perlite material.
 5. A method of at leastsubstantially eliminating Cryptosporidium organisms from pool watercomprising the steps of: passing pool water through a sand filter togenerate filtered pool water, wherein the sand filter includes a filtermedia comprising a bed of sand that is disposed on a bottom of a tank ofthe filter and a layer of perlite material that is disposed on a topsurface of the bed of sand, the perlite material being a high flow rate,low density perlite material that only contains a trace amount offloaters.
 6. The method of claim 5, wherein the perlite material isadded in an amount of ¼ lb per sq. ft. of filter surface area.
 7. Themethod of claim 5, wherein the filtered water is at least 98% free ofthe Cryptosporidium organisms.
 8. The method of claim 5, wherein betweenabout 97% and about 99% of the Cryptosporidium organisms are removedfrom the filtered water by passing the pool water through the sandfilter.
 9. A method of forming a sand/perlite layered filter media in asand filter that is part of a swimming pool that includes a skimmer,comprising the steps of: adding sand to the bottom of a tank of the sandfilter to form a bed of sand; operating the sand filter so that waterpasses therethrough; and adding a predetermined amount of perlitematerial through an inlet of the skimmer that is in communication withpool water, while the sand filter is operating, resulting in the perlitematerial being added as a layer to a top surface of the bed of sand. 10.The method of claim 9, wherein the perlite material is a high flow rate,low density perlite material that only contains a trace amount offloaters.
 11. The method of claim 9, wherein the perlite material has aspecific gravity of about 2.3; a wet apparent density between about 8.5to 9.5 lbs/cubic foot; a loose weight density between about 5.5 to 6.5lbs/cubic foot; and a Darcy units of about 3.25.
 12. The method of claim9, wherein a weight of the perlite material is about 0.25 lbs/ft². 13.The method of claim 9, wherein the layer of perlite material comprises acake structure of perlite material.
 14. The method of claim 9, whereinthe perlite material is prepackaged in a package that includes a labelthat equates the amount of perlite material in the package to a squarefootage of the filter.